Generally, digital components have input and output ports which enable the exchange of signals with neighboring components. As an example, communication between a microprocessor and a random access memory (RAM) may be mentioned.
In the search for high performance, increasing the operating frequency of the processor may be desirable, and thus the frequency of exchanges with neighboring components. At a certain level, the characteristic impedance of the connection between the output of a component and the input of the neighboring component may have an influence on the quality of the transmitted signal. In other words, it may be advantageous for the input or output impedance of an input or output port to be calibrated.
Various specifications exist depending on the technology used, which may set the optimal input or output impedance value, as well as the tolerances. To respect these specifications, it may be desirable to calibrate the output impedance of the concerned output ports, since it may depend on multiple factors. One can, in particular, mention factors associated with the component manufacturing process, or factors capable of varying along with the circuit operation, and in particular, the temperature of use, or the value of the power supply voltage for an autonomous device. Calibration of the output impedance of a digital port has already been provided by selecting an appropriate number of active transistors in a buffer or driver stage between a control terminal of the output signal and the actual output terminal.